An agitator-grinder of this general kind, having an annular-cylindrical grinding chamber located between an agitator mechanism on one side, embodied by an agitator shaft with a hollow, cylindrical body, and the inner wall of the grinder vessel on the other is already known from German examined application DE-AS No. 11 84 188. Narrow annular-cylindrical grinding chambers of this kind, with a gap width of approximately 5 to 15 mm, have the advantage that the individual particles of a grinding stock in suspension or dispersion are very uniformly exposed to grinding and shear forces, so that there is a very small variation in the fineness of grinding. Because the radial extension of the grinding chamber per se is quite small, the auxiliary grinding bodies tend to back up at the separator because a sufficient return flow is not assured, although during the grinding process the auxiliary grinding bodies are capable of moving freely within the flow of auxiliary grinding bodies and auxiliary grinding stock taking place in the annular-cylindrical grinding chamber.
In order to attain a recirculation of the auxiliary grinding bodies back from the outlet for the ground stock, or in other words from the vicinity of the separator device, it is already known from British Pat. No. 2,016,953, relating to an agitator-grinder having an agitator mechanism which is embodied by discs on an agitator shaft, to make holes in these discs which have a radial component, so that the auxiliary grinding bodies entering such a hole in a disc from the top will be accelerated in their downward movement, thus creating a kind of return flow conduit.
An agitator-grinder having a means of recirculating auxiliary grinding bodies is known from German laid-open applications DE-OS No. 28 11 899. This apparatus functions on the same principle; that is, one or more return flow conduits having a radial directional component are provided in the agitator mechanism.
This known principle of returning auxiliary grinding bodies has the disadvantage that it is impossible to exert influence on the recirculation of the auxiliary grinding bodies, because their recirculation is effected by means of the agitator mechanism, which is drivable at high speed and, in the case of a closed agitator-grinder, is practically inaccessible.